Apart from family and existing friends (our initial social graph) we follow others because there is sufficient cross-over in our interests so, somewhat ironically, the interest graph is actually the primary driver behind expanding the social graph.

Data

There is great play to get us to populate the social services without needing to actively engage on them:

Plus - a social layer, integrating across the Google ecosystem so that we don't need to visit the social network

Facebook - the open graph, filling our timelines with data without ever having to visit Facebook itself

A flood of +1s and Likes expanding our interest graphs.

So, what is engagement?

Is it actually contributing to the social networks directly or can it be interpreted as any interaction via any means on a “socially connected” service or site?

This then leads us to ask about the definition of an active account and how social networks use this loose definition to bolster user numbers.

Encroachment

Search Plus Your World and, now, Bing social search are bringing social into our everyday lives - the distinction between the social web and the normal web is disappearing. With location and situational context the separation between online and offline is also narrowing.